As shown in FIG. 9, a cathode ray tube 20 is basically composed of a glass panel for displaying an image 1, and a glass bulb including a glass funnel 2 having a neck portion 5 for housing an electron gun 6.
Referring to FIG. 9, the glass funnel 2 includes a body portion 3 having an open end for connection with the glass panel 1, the neck portion 5 for housing the electron gun 6, and an yoke portion connecting between the body portion and the neck portion and having an outer side configured so as to mount a deflection coil (deflection yoke) as a deflection unit for deflecting electron beams irradiated from the electron gun thereon. In FIG. 9, reference numeral 10 designates a sealing portion for sealing the glass panel 1 to the glass funnel 2 with solder glass or the like, reference numeral 11 designates an electron beam, reference numeral 12 designates a fluorescent film for emitting fluorescence by irradiation of electron beams 11, reference numeral 13 designates an aluminum film for reflecting forwardly light emitted from the fluorescent film, reference numeral 14 designates a shadow mask for determining the position of irradiated electron beams on the fluorescent film, reference numeral 15 designates a stud pin for fixing the shadow mask 14 to an inner surface of the glass panel 1, reference numeral 16 designates a reinforcing band for maintaining strength against impact, and reference numeral 17 designates an anode button, which is connected to outside for grounding so as to prevent the shadow mask 14 from being charged at a high potential by irradiation of electron beams 11.
Reference A designates a bulb axis, which connects between the central axis of the neck portion 5 and the center of the panel portion 3, and reference B designates an imaginary reference line, which indicates the center of deflection. The screen that is made of the fluorescent film 12 on the inner surface of the glass panel has a substantially rectangular shape having the bulb axis at the central point and is defined by 4 sides substantially parallel to a long axis or a short axis which cross perpendicular to the bulb axis.
The inside of the cathode ray tube is maintained under high vacuum to display an image by irradiation of electron beams in the glass bulb. The cathode ray tube not only has high deformation energy (strain energy) inherent therein since the cathode ray tube has an asymmetric structure, unlike a spherical shape, wherein a differential pressure of 1 atmospheric pressure is applied between the inside and the outside thereof. Additionally, the cathode ray tube is deformed in an unstable fashion. When the glass is cracked forming the cathode ray tube in such a state, the crack will extend to release the high deformation energy inherent in the cathode ray tube, finally fracturing the cathode ray tube in some cases. Further, in such a condition that a high stress is applied to an outer surface of the cathode ray tube, delayed fracture (fracture caused after lapse of a period of time) may occur due to the action of moisture in the atmosphere, making it impossible to display an image, in some cases.
Various kinds of display devices, such as liquid crystal display devices and plasma display devices, other than cathode ray tubes, have been recently proposed. In comparison with display devices other than cathode ray tubes, it is pointed out that the display devices comprising a cathode ray tube have a main disadvantage of having a long depth. Although it is desired to decrease the depth in the cathode ray tubes from this viewpoint, a reduction in the depth increases the asymmetry in the structure of the cathode ray tubes, and tensile stresses generated in an outer surface are apt to increase. In particular, an increase in the tensile stresses is also significant in the yoke portion where deformation energy given by deformation in the body portion concentrates.
An increase in the tensile stresses brings about a decrease in reliability because of a reduction in safety by fracture or because of delayed fracture. On the other hand, when the glass thickness of the body portion is increased to prevent the tensile stresses from increasing, the mass of the body portion is further increased. When the glass thickness of the yoke portion is increased, the yoke portion necessarily needs to project inwardly in order to mount a deflection coil on the outer side thereof, causing, e.g., a serious problem that electron beams impinge on an inner surface of the yoke portion to significantly degrade image quality.
It is an object of the present invention to provide a cathode ray tube and a glass funnel applicable to the cathode ray tube, which are capable of being safe, highly reliable and lightweight, wherein a tensile stress, which is generated in the yoke portion or the body portion of a glass funnel to cause fracture in the yoke portion, can be prevented from increasing without increasing the glass thickness of the body portion or the yoke portion.